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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    Biasing - Ultralinear vs Triode mode.

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    boeingpilot


    Posts : 34
    Join date : 2015-06-21
    Location : Central PA

    Biasing - Ultralinear vs Triode mode. Empty Biasing - Ultralinear vs Triode mode.

    Post by boeingpilot Sat Oct 30, 2021 5:28 am

    As mentioned elsewhere, I just picked up a Panor/Dynaco ST80. Set the bias per the manual while it was set to ultralinear mode. Switching the amp to triode mode, the indicators indicate that the bias is low. (Personally like the way this sounds in triode over ultralinear).

    As I suspect the topology is similar to the VTA amps, should I leave the bias as set with ultralinear selected, or rebias with the amp in triode mode?

    Thoughts?
    ttocs
    ttocs


    Posts : 41
    Join date : 2019-05-20
    Location : Northern Illinois

    Biasing - Ultralinear vs Triode mode. Empty Re: Biasing - Ultralinear vs Triode mode.

    Post by ttocs Sat Oct 30, 2021 6:03 am

    I've seen the same thing happen with my M-125. It's only a little over +0.03V difference if I bias to 1V while in Triode mode, then switch to UL.

    So I guess it would matter more if the line voltage is a tad on the "hot" side. Personally, I use a Variac and strive to keep the volts to about 115V-117V, so the extra few hundredths of a volt isn't a problem from what I've measured internally. So, going in the opposite direction like you've stated also shouldn't be a problem.
    avatar
    boeingpilot


    Posts : 34
    Join date : 2015-06-21
    Location : Central PA

    Biasing - Ultralinear vs Triode mode. Empty Re: Biasing - Ultralinear vs Triode mode.

    Post by boeingpilot Sat Oct 30, 2021 6:29 am

    Therein lies the issue... On the Panor ST80, all I have to set by is the LEDs. I actually have no idea what the voltage (hence current) is. Kind of wish they had provided test points as well.

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    Biasing - Ultralinear vs Triode mode. Empty Re: Biasing - Ultralinear vs Triode mode.

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